linux-kernel - Re: [PATCH 0/10] Reduce system disruption due to kswapd V2

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Message-ID: <5174DA8F.2020400@bitsync.net>
Date:	Mon, 22 Apr 2013 08:37:03 +0200
From:	Zlatko Calusic <zcalusic@...sync.net>
To:	Mel Gorman <mgorman@...e.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	dormando <dormando@...ia.net>,
	Satoru Moriya <satoru.moriya@....com>,
	Michal Hocko <mhocko@...e.cz>, Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/10] Reduce system disruption due to kswapd V2

On 12.04.2013 22:07, Zlatko Calusic wrote:
> On 12.04.2013 21:40, Mel Gorman wrote:
>> On Thu, Apr 11, 2013 at 10:55:13PM +0200, Zlatko Calusic wrote:
>>> On 09.04.2013 13:06, Mel Gorman wrote:
>>> <SNIP>
>>>
>>> - The only slightly negative thing I observed is that with the patch
>>> applied kswapd burns 10x - 20x more CPU. So instead of about 15
>>> seconds, it has now spent more than 4 minutes on one particular
>>> machine with a quite steady load (after about 12 days of uptime).
>>> Admittedly, that's still nothing too alarming, but...
>>>
>>
>> Would you happen to know what circumstances trigger the higher CPU
>> usage?
>>
>
> Really nothing special. The server is lightly loaded, but it does enough
> reading from the disk so that pagecache is mostly populated and page
> reclaiming is active. So, kswapd is no doubt using CPU time gradually,
> nothing extraordinary.
>
> When I sent my reply yesterday, the server uptime was 12 days, and
> kswapd had accumulated 4:28 CPU time. Now, approx 24 hours later (13
> days uptime):
>
> root        23  0.0  0.0      0     0 ?        S    Mar30   4:52 [kswapd0]
>
> I will apply your v3 series soon and see if there's any improvement wrt
> CPU usage, although as I said I don't see that as a big issue. It's
> still only 0.013% of available CPU resources (dual core CPU).
>

JFTR, v3 kswapd uses about 15% more CPU time than v2. 2:50 kswapd CPU 
time after 6 days 14h uptime.

And find attached another debugging graph that shows how ANON pages are 
privileged in the ZONE_NORMAL on a 4GB machine. Take notice that the 
number of pages in the ZONE_DMA32 is scaled (/5) to fit the graph nicely.

-- 
Zlatko

Download attachment "memdebug-daily.png" of type "image/png" (17239 bytes)